Rotary encoder
An encoder (or angle of rotation sensor or rotary encoder ) is a sensor for angle of rotation , which is usually digital output signals supplies, which must be decoded at the other end of the sensor line in the device. That is why it is also known as an encoder (rotary encoder).
"Rotary encoder" is sometimes used as a generic term for all angular position encoders .
Differences in the type of signal evaluation
Incremental encoder
Incremental encoders deliver a certain number of pulses per revolution as well as a so-called zero pulse per revolution. Here the acquisition takes place via a reticle, magnetic wheel (pole wheel) or gear wheel flanks . Two digital output signals (A and B track) or analog sine or cosine signals are outputted by a quarter pulse (90 ° electrical) . The value is generated by counting the pulses in the evaluation device. The absolute angle can only be determined after processing the reference mark or recognizing the marking of the zero point (zero pulse). By recognizing the signal edge, one signal can be calculated as a “clock” or “step” and another for the “direction”. Incremental encoders are often used as a tachometer by measuring the time of a revolution (time between two zero pulses) or an increment.
Incremental encoder with UVW signals
In the case of an incremental encoder with UVW signals , in addition to the AB tracks of the incremental encoder ( encoder ) there are also so-called U, V and W tracks.
These are usually used for commutation in electrical three-phase machines . The UVW signals change during the rotary movement according to the 3-bit Gray code , with the states [000] and [111] not occurring. In a three-phase machine with only one pair of poles, six states are distinguished per mechanical revolution. This means that the rotor position is known precisely to at least 60 °, which is sufficient to move the three-phase machine with field-oriented control up to the next UVW edge. The exact rotor position is then known there.
Absolute encoder
With the absolute encoder , the acquisition takes place via a coding disc. Several revolutions are recognized by a built-in gear or other method (e.g. Wiegand wire ), followed by the serial transmission of the measured values to the evaluation device. The measured value is available immediately after switching on.
Differences in the mechanical structure
- Encoder with own storage
- one-sided or through hollow shaft with attached stator coupling . They are plugged directly onto the shaft to be measured.
- with short shaft (Ø 4/6/10 mm) and synchro flange or clamping flange. They are connected with a separate shaft coupling (see picture).
- Encoder without own storage, e.g. B. Built-in rotary encoders or built-in measuring devices. With them, the rotor is mounted directly on the shaft to be measured. The stator must be aligned with the machine for this.
